Disk array storage systems include a plurality of hard disk drives, such as the 51/4 or 31/2 inch disk drives currently used in personal computers and workstations, which operate in parallel and appear to the host system as a single large disk drive. Numerous disk array design alternatives are possible, incorporating a few to many disk drives. Several array alternatives, each possessing different attributes, benefits and shortcomings, are presented in an article titled "A Case for Redundant Arrays of Inexpensive Disks (RAID)" by David A. Patterson, Garth Gibson and Randy H. Katz; University of California Report No. UCB/CSD 87/391, December 1987. The article, incorporated herein by reference, discusses disk arrays and the improvements in performance, reliability, power consumption and scalability that disk arrays provide in comparison to single large magnetic disks.
Complex storage management techniques are required in order to coordinate the operation of the multitude of data storage devices within an array to perform read and write functions, parity generation and checking, data restoration and reconstruction, and other necessary or optional operations. Array operation can be managed by a dedicated hardware controller constructed to control array operations, i.e., a hard array architecture, or through software routines executed by the host computer system, i.e., a software array architecture.
A hardware array improves data storage reliability and availability, and increases system performance without modifying user applications. A hardware controller removes many of the data storage tasks from the host system processor, permitting greater accommodation of other applications and tasks by the host system.
A software architecture allows existing system hardware and storage devices to be utilized as an array storage system. The increasing speed and power of advanced computer systems provides performance that is competitive with many hardware array products. A software array architecture can deliver this functionality at a lower cost of implementation than a hardware array. Greater configuration flexibility may also be provided. However, the host processor remains burdened with data storage tasks.
The hardware and software array alternatives discussed above provide improvements in performance, reliability, power consumption, scalability and capacity in comparison to single large magnetic disks. However, coincident with these improvements there exists a need to store and manage ever increasing amounts of data, and to utilize the host processor, array controller and storage devices in the most efficient and effective manner. Additional improvements to data storage systems are desired to better utilize the speed and power of current and next generation computer systems, particularly multiple processor computer systems.